This invention relates to a process for the recovery of 2-pyrrolidone from an alkaline aqueous solution containing the same. More particularly, this invention relates to a process for the recovery of unreacted 2-pyrrolidone, of sufficiently high purity to be polymerizable with normal treatment, from the wash water used to remove the alkaline catalyst from an incompletely reacted polypyrrolidone polymerizate. 2-pyrrolidone has a normal boiling point of 245.degree. C and is readily and completely miscible with water.
In polymerizing 2-pyrrolidone using an alkaline catalyst, the recovery of unreacted pyrrolidone may be accomplished by several methods all of which begin by washing the incompletely reacted polymerizate with water or a water-miscible solvent to extract the alkaline catalyst and unreacted pyrrolidone. The resulting alkaline aqueous pyrrolidone-containing solution may be directly distilled, but this is found to produce a gel-like residue which limits the recoverability of 2-pyrrolidone and furthermore, the alkali tends to hydrolyze the 2-pyrrolidone. Alternatively, the alkaline aqueous solution of 2-pyrrolidone may be separated into two phases, one of which is richer in 2-pyrrolidone, by the addition of certain inorganic salts; however, this does not solve the problem of complete recovery of 2-pyrrolidone. Furthermore, the phase-separation method was found to be particularly applicable to potassium-containing alkaline solutions and impractical for sodium-containing solutions.